Adsorption of organic friction modifier additives
File(s)
Author(s)
Fry, Ben
Moody, Gareth
Spikes, Hugh A
Wong, Janet SS
Type
Journal Article
Abstract
Organic friction modifier additives (OFMs) are surfactant molecules added to engine oils to reduce friction in the boundary lubrication regime. They are thought to work by forming an absorbed layer which provides low friction. This paper studied the relationship between the adsorption of OFMs and their friction and wear reducing properties in a rubbing contact formed by a stationary glass ball and a rotating silicon disk under the boundary lubrication regime. The effect of molecular structure was investigated by using OFMs of various tail saturation and head group chemistry. OFM tested were oleic acid, octadecylamine, oleylamine and glycerol monooleate. The thickness of an OFM adsorbed layer in hexadecane, examined in-situ by spectroscopic ellipsometry and quartz crystal microbalance (QCM), depends on the molecular structure and the concentration of the OFM. As expected, saturated, linear chain gives the thickest film. A critical OFM layer thickness of about 0.6 nm is necessary to achieve low initial and maximum friction. The thicker OFM layers are accompanied by narrower wear tracks, which are rougher than the wider, smoother wear tracks formed with thinner OFM layers. The interplay between the thickness of the OFM layer and wear track surface roughness results in all OFM layers having similar steady friction. This shows that the apparent effect of OFM depends on the stage of rubbing test: initially on friction; and then subsequently on surface damage. Despite OFMs and the base oil having similar refractive indices, ellipsometry was found to be a suitable technique for examining the adsorption of OFM additives from an oil based solution, and showed reasonable correlation with QCM results.
Date Issued
2020-02-11
Date Acceptance
2020-01-15
Citation
Langmuir, 2020, 36 (5), pp.1147-1155
ISSN
0743-7463
Publisher
American Chemical Society (ACS)
Start Page
1147
End Page
1155
Journal / Book Title
Langmuir
Volume
36
Issue
5
Copyright Statement
© 2020 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that will appear in final form in Langmuir, after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.langmuir.9b03668.
Sponsor
Croda Europe Limited
Engineering & Physical Science Research Council (EPSRC)
Identifier
https://pubs.acs.org/doi/10.1021/acs.langmuir.9b03668
Grant Number
Mr Benjamin Fry
EP/P030211/1
Subjects
Science & Technology
Physical Sciences
Technology
Chemistry, Multidisciplinary
Chemistry, Physical
Materials Science, Multidisciplinary
Chemistry
Materials Science
SELF-ASSEMBLED MONOLAYERS
SPECTROSCOPIC ELLIPSOMETRY
BOUNDARY LUBRICATION
ENERGY-DISSIPATION
ALKANE SOLUTION
STEARIC-ACID
FATTY-ACIDS
FILMS
SURFACE
SILICON
Chemical Physics
Publication Status
Published online
Article Number
acs.langmuir.9b03668
Date Publish Online
2020-01-15